Neurological features of Hansen disease: a retrospective, multicenter cohort study

To elucidate the neurological features of Hansen disease. The medical records of patients with confirmed Hansen disease transferred from the neurology department were reviewed, and all medical and neurological manifestations of Hansen disease were assessed. Eleven patients with confirmed Hansen disease, 10 with newly detected Hansen disease and 1 with relapsed Hansen disease, who visited neurology departments were enrolled. The newly detected patients with Hansen disease were classified as having lepromatous leprosy (LL, n = 1), borderline lepromatous leprosy (BL, n = 2), borderline leprosy (BB, n = 2), borderline tuberculoid leprosy (BT, n = 1), tuberculoid leprosy (TT, n = 2), or pure neural leprosy (PNL, n = 2). All of the patients with confirmed Hansen were diagnosed with peripheral neuropathy (100.00%, 11/11). The symptoms and signs presented were mainly limb numbness (100.00%, 11/11), sensory and motor dysfunction (100.00%, 11/11), decreased muscle strength (90.90%, 10/11), and skin lesions (81.81%, 9/11). Nerve morphological features in nerve ultrasonography (US) included peripheral nerve asymmetry and segmental thickening (100.00%, 9/9). For neuro-electrophysiology feature, the frequency of no response of sensory nerves was significantly higher than those of motor nerves [(51.21% 42/82) vs (24.70%, 21/85)(P = 0.0183*)] by electrodiagnostic (EDX) studies. Nerve histological features in nerve biopsy analysis included demyelination (100.00%, 5/5) and axonal damage (60.00%, 3/5). In addition to confirmed diagnoses by acid-fast bacteria (AFB) staining (54.54%, 6/11) and skin pathology analysis (100.00%, 8/8), serology and molecular technology were positive in 36.36% (4/11) and 100.00% (11/11) of confirmed patients of Hansen disease, respectively. It is not uncommon for patients of Hansen disease to visit neurology departments due to peripheral neuropathy. The main pathological features of affected nerves are demyelination and axonal damage. The combination of nerve US, EDX studies, nerve biopsy, and serological and molecular tests can improve the diagnosis of Hansen disease.

In addition, F-wave abnormalities were found in 3 patients; no response was observed in 1 patient, prolonged latency was observed in 2 patients, and a decreased frequency was observed in 1 patient.The H-reflex was normal in 7 patients.However, SSRs were not detected in 2 patients.EMG demonstrated neurogenic damage in 10 patients (Table 4).
In terms of special staining of nerve biopsy, samples from 2 patients underwent AFB staining, with negative results for both (0.00%, 0/2).Samples from two patients underwent weak acid-fast staining; a positive result was found for 1 patient (50.00%, 1/2), while a negative result was found for the other patient.

Hansen disease symptom monitoring criteria
All patients with Hansen disease were evaluated with the Hansen disease Symptom Monitoring criteria (Supplementary Table S1), and those meeting the criteria of suspected Hansen disease were transferred from the neurology departments to the Hansen disease prevention facility.

Confirmed diagnosis of Hansen disease
Hansen disease was confirmed in eleven patients, including 10 patients with newly detected and 1 patient with relapse, according to the diagnostic criteria for Hansen disease in WHO 10 .The details are shown in Table 9.

Discussion
Hansen disease is a chronic infection caused by Mycobacterium leprae that is associated with peripheral neuropathy.Early Hansen disease detection and treatment with multidrug therapy are the most important steps in preventing deformity and disability 11 .
The gold standard for Hansen disease diagnosis is dermatological and neurological clinical examination, bacilloscopy/AFB staining of the SSS and skin biopsy sample analysis 12,13 .To confirm the diagnosis, laboratory tests, AFB staining, skin and nerve biopsy, and serological and molecular tests were performed for all of the patients.In this study, the diagnoses of 11 patients with Hansen disease were confirmed: as 1 LL, 2 BL, 2 BB, 1 BT, 2 TT, 2 PNL, and 1 relapsed.The diagnoses of six (1 LL, 2 BL, 2 BB and 1 relapsed) patients were confirmed by AFB staining, and the diagnoses of 8 (1 LL, 2 BL, 2 BB, 1 BT, 1 TT, and 1 relapsed) patients were confirmed by skin biopsy.AFB staining results were negative in 1 TT and 2 PNL patients, and skin biopsy was not suitable for some TT or PNL patients, which implies the limited diagnostic value of traditional laboratory tests for Hansen disease.Notably, the nerve biopsy sample of 1 (BB) patient was positive for AFB staining, which provided morphological evidence of Mycobacterium leprae infection in the in situ nerve tissue.
Since the 1980s, components isolated from M. leprae have been identified 14,15 ; an increasing number of experimental trials have used these components to detect antibodies in Hansen disease patients.These detection methods are mainly used for diagnosing MB of Hansen disease, monitoring treatment response, and predicting leprosy reactions and as active search strategies to identify new cases in high-risk populations [16][17][18][19] .
In the past three decades, definitive identification of M. leprae has been possible through the development of methods for the extraction, amplification, and identification of M. leprae DNA in clinical specimens via PCR.high sensitivity and specificity for early diagnosis 24 .In our previous study, we also observed a combination of an enlarged CSA of nerves in the upper limbs and atrophy of lower limb nerves in clinically cured Hansen disease patients 30 .In addition to an abnormal CSA, a loss of fascicles, hypoechogenicity and increased neural vascularity have also been reported in patients with Hansen disease 22 .In this study, asymmetrical and segmental thickening, swelling, and abnormal signs of echo intensity and blood flow were detected via nerve ultrasonography.The US results in our study are consistent with those of previous reports.The risk factors for nerve enlargement in patients with Hansen disease were MB leprosy 25 , leprosy reaction 26 , neuritis 27 , and impairment of function 28 .Nerve ultrasonography for Hansen disease can be applied in the early diagnosis of Hansen disease in household contacts (HHCs) 29 and for monitoring the therapeutic effects of MDT 27 .Compared with healthy volunteers, individuals with at least two thickened nerves assessed in the active search campaign had a 23.1 greater chance of having Hansen disease than healthy individuals 24 .Nerve ultrasonography showed greater sensitivity than clinical examination for detecting peripheral nerve thickening in Hansen disease patients, which may therefore improve the sensitivity of the diagnostic criterion of peripheral nerve enlargement in the diagnosis and classification of Hansen disease 28 .In this study, we also demonstrated that, when compared with the results of nerve ultrasonography, nerve palpation lacks precision in detecting nerve thickness.Due to the very limited accuracy of nerve palpation, the systematic and comprehensive development of nerve ultrasonography for both Hansen disease patients and close contacts is needed.www.nature.com/scientificreports/Abnormal nerve conduction in patients with Hansen disease was characterized by reduced conduction velocities in addition to changes in prolonged distal latency and decreased amplitude in the affected nerves [31][32][33] .Sensory latency and amplitude changes were more severe than motor latency and amplitude changes in patients presenting with muscle palsies 32,33 .Patients with the TT type of Hansen disease were the most affected 33,34 .Electrophysiological testing showed both axonal and demyelinating nerve involvement 35,36 .
The number of nerve abnormalities detected by electrophysiological testing is significantly greater than that detected clinically 36 .In Hansen disease patients, motor weakness, sonographic thickening, and motor conduction abnormalities are positively correlated 37 .An approach combining nerve ultrasonography and electrophysiological testing can improve Hansen disease diagnosis 38 .
Nerve histology is studied less often than cutaneous histology.Depending upon the host immune response, a spectrum of pathological changes in the skin are reflected in nerves.At the tuberculoid end of the spectrum, epithelioid granulomas with little or no AFB staining are observed, while at the lepromatous end, abundant AFB staining of Schwann cells, macrophages and plasma cell infiltrates are observed 39 .Other nerve changes include mild perineural edema, partial involvement of fascicles, a loss of fiber density and areas of demyelination 40 .Demyelination can occur primarily at the site of acute neuritis or secondary to chronic axonopathy.In severe cases, there is destruction of the nerve parenchyma with caseous necrosis with epithelioid infiltrates and segmental necrotizing granulomatous neuritis 41 .During spontaneous or posttreatment regression of nerve lesions, residual signs of chronic inflammation with lymphocytic infiltration and evidence of regeneration and fibrosis are observed 42 .The results of nerve biopsy in this study were consistent with those of previous studies.
Along with peripheral nerves, the central nervous system (CNS), spinal root ganglion and brachial plexus are involved in Hansen disease 43,44 .MBP, an indispensable protein of myelinated axons, is abundant in CNS myelin and has long been studied as a factor in the pathogenesis of neurodegenerative diseases, such as multiple sclerosis (MS) 45 and reported in Hansen disease 46 .In this study, demyelination in the periventricular white matter of the lateral ventricle was detected by MRI in one patient, and MBP IgG was elevated in another patient.This finding provides evidence of demyelination in the CNS and peripheral nervous system in patients with Hansen disease.

Conclusion
Hansen disease patients may visit the neurology department due to neurological manifestations.Patients with peripheral neuropathy with or without skin lesions, after excluding other causes, were considered suspected to have Hansen disease.
The ultrasonographic features of Hansen disease included asymmetrical and segmental patterns of increased CSA.The electrophysiological features included no response, reduced conduction velocities, prolonged latency and decreased amplitude in the affected nerves.Nerve pathological features included AFB staining; axon and myelin sheath destruction; Schwann cell hyperplasia or an absence of macrophage, plasma cell, and/or lymphocyte infiltration; fibrosis; and edema.
The combination of ultrasonographic and electrophysiological testing with serological and molecular testing may improve the diagnosis of Hansen disease.Nerve biopsy can be chosen for difficult cases of PNL when the diagnosis is unclear and to provide in situ evidence for the pathogen in nerve tissue.

Table 2 .
Results of neurologic examination for confirmed patients with Hansen disease who visited the neurology department.Significant values are in bold.L left, R right, (+) positive, (−) negative.

Table 4 .
The electrodiagnostic study results for the confirmed patients with Hansen disease enrolled in this study.NCV nerve conduction velocity, SSR skin symptomatic response, EMG electromyography, ND not described, LLN lower limit of normal.Vol.:(0123456789) Scientific Reports | (2024) 14:10374 | https://doi.org/10.1038/s41598-024-60457-0www.nature.com/scientificreports/Indexes for differential diagnosis Other indexes, including indices of metabolism, rheumatism, immunity, nutrition, drugs, toxicity, tumors, infection, physical compression, the blood system, and the nervous system, were screened for the differential diagnosis of Hansen disease from neuropathy (Table 8).The indicators of Rheumatism & Immunity were positive in 37.50% (3/8) patients, involved positive results of Proliferating Cell Nuclear Antigen (PCNA) in case 4, Anti streptolysin O (ASO) in case 10, and Antinuclear antibody (ANA) in case 11, respectively.As an indicator of CNS demyelination, MBP IgG was also increased in Patient 4, and demyelination in the periventricular white matter of the lateral ventricle was detected by magnetic resonance imaging (MRI) in Patient 11.All the other results were negative.

Table 5 .
The nerve conduction velocity of the confirmed patients with Hansen disease enrolled in this study.NCV Nerve conduction velocity.*P < 0.05.

Table 6 .
The nerve biopsy results of confirmed patients with Hansen disease enrolled in this study.ND not described, (+): positive; (−): negative.

Table 8 .
Indexes for the differential diagnosis of Hansen disease from neuropathy.

Table 10 .
Worsening disability in the multiple medical records of patients with Hansen disease.

Table 12 .
Deteriorated nerve conduction in the Multiple medical records of the patients with Hansen disease.ND not described.Up arrow (↑): increased; down arrow (↓): decreased.